Derivative Instruments and Hedging Activities - Cumulative Basis Adjustment for Fair Value Hedges (Detail) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
AFS debt securities
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amortized Cost	$ 22,500	$ 22,500
Unamortized basis adjustments from interest rate swaps designated as fair value hedges of long-term advances from FHLB	(1,331)	1,777
Deposits
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amortized Cost	300,000	0
Unamortized basis adjustments from interest rate swaps designated as fair value hedges of long-term advances from FHLB	1,787	0
FHLB advances
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amortized Cost	700,000	0
Unamortized basis adjustments from interest rate swaps designated as fair value hedges of long-term advances from FHLB	$ (10,160)	$ 0